Design Tips and Key Points for Efficient Automated Routing of PCBs (I)

Although the current EDA tools are very powerful, as PCB size requirements become smaller and the device density becomes higher and higher, PCB design is not difficult. How to achieve high PCB throughput and shorten design time? This article describes the design tips and key points of PCB planning, layout, and routing.

Nowadays PCB design is getting shorter and shorter, smaller and smaller board space, higher device density, extremely harsh layout rules and large size components make the designer's work more difficult. In order to solve the design difficulties and speed up the market launch, many manufacturers now prefer to use dedicated EDA tools to achieve PCB design. However, dedicated EDA tools do not produce the desired results, nor can they achieve 100% throughput, and they are messy, and usually take a lot of time to complete the rest of the work.

There are a lot of EDA tools available on the market, but they are similar except for the terms and function keys used. How to use these tools to better design the PCB? Careful analysis of the design and careful setup of the tool software before starting the wiring will make the design more compliant. Below are the general design procedures and procedures.

1. Determine the number of layers of the PCB

Board size and number of wiring layers need to be determined early in the design process. If the design requires the use of high-density ball grid array (BGA) components, the minimum number of routing layers required for wiring these devices must be considered. The number of wiring layers and the stack-up method directly affect the wiring and impedance of the printed wiring. The size of the board helps determine the stacking and line width to achieve the desired design.

For many years, people have always thought that the lower the number of board layers, the lower the cost, but there are many other factors that affect the manufacturing cost of the board. In recent years, the cost difference between multilayer boards has been greatly reduced. At the beginning of the design, it is better to use more circuit layers and evenly distribute the copper to avoid a small number of signals that do not meet the defined rules and space requirements at the end of the design, and thus be forced to add new layers. Careful planning before design will reduce a lot of trouble in wiring.

2. Design rules and restrictions

The autorouting tool itself does not know what to do. To complete the routing task, the routing tool needs to work under the correct rules and constraints. Different signal lines have different wiring requirements, and all special required signal lines are classified, and different design classifications are also different. Each signal class should have priority. The higher the priority, the stricter the rules. The rules relate to the width of the trace, the maximum number of vias, the parallelism, the interaction between the signal lines, and the limitations of the layers, which have a large impact on the performance of the routing tool. Careful consideration of design requirements is an important step in successful cabling.